The title of this proposal captures its essence, "Hazardous Waste Risk and Remediation in the Southwest". The University of Arizona Superfund Basic Research Program renewal application builds on the achievements of the previous grant. The theme of this Program is to support development of a risk assessment process for metal and organic contaminants through toxicologic and hydrogeologic studies and through development of innovative remediation technologies. Our application emphasizes hazardous waste issues in the Southwestern U.S. (and Mexican Border) due to the unique arid nature of this environment. However, the results of our studies are not limited to the Southwest since the main toxicants being examined, arsenic and halogenated hydrocarbons, are ubiquitous throughout developed countries. Our Program consists of 10 research projects - five biomedical projects and five environmental sciences projects. Many of the projects are collaborative involving multiple disciplines. The biomedical projects are examining the mechanism of arsenic toxicity in target tissues, factors that affect the susceptibility of populations to arsenic-induced toxicity, and the effects of arsenic and TCE on organ development. The environmental sciences projects are investigating how hazardous wastes (arsenic, TCE/PCE) can be optimally characterized for remediation and innovative techniques for containing or degrading these contaminants in our arid Southwest environment. These research projects are supported by five Cores that: administer the Program, translate the results to the stakeholders, provide research services, promote unique outreach efforts to Mexico, and support graduate student training. This project will contribute to our understanding of toxicology and remediation of hazardous wastes nationally and internationally.